See-through display

ABSTRACT

A screen includes a first set of louver members at least partially disposed in the screen and located proximate to a first side of the screen, and a second set of louver members at least partially disposed in the screen and located proximate to a second side of the screen. An observer on either side of the screen sees an image produced by light directed to that observer by that set of louvers on the same side of the screen as the observer. Objects on the other side of the screen from the observer are visible to the observer between the louvers.

RELATED APPLICATION

This is a divisional patent application which claims priority under 35U.S.C. 120 from previous U.S. patent application Ser. No. 11/491,360,filed Jul. 21, 2006 now U.S. Pat. No. 8,212,744, entitled “See ThroughDisplay,” which is incorporated herein by reference in its entirety.

BACKGROUND

Socially and professionally, most people rely on visual display systemsof one form or another for at least a portion of their work and/orrecreation. Typical displays, such as cathode ray tubes (CRTs), plasmadisplay panels (PDPs) and the like are opaque, or at the very leastblock the view of background objects directly behind the display system.

See-through display technology for the display of text messages has beenadvancing, but is primarily limited to the fields of advertising andteleprompting for news and presentation. In advertising, such systemsare desirable as they permit a customer to receive text informationwhile viewing actual items such as retail clothing. For news media,teleprompters permit the presenting party to appear as though he or sheis maintaining eye contact with the audience. Heads-up see-throughdisplays are also evolving in for use in aircraft and automobiles asthey permit the operator of the plane or vehicle to maintain visualawareness of the outside environment while receiving importantinformation such as speed, direction, remaining fuel, etc.

These see-through display systems or heads-up displays are typicallyachieved by using a transparent piece of glass or plastic mounted at aforty five degree angle. In some configurations there is also a thincoating of reflective material, sufficient to establish a half mirror.With such systems, the projected information is presented only to oneside of the display. Thus, for example, the audience does not see thespeech scrolling across the teleprompter.

Such systems are reasonably good for high contrast material such asbright text, or images formed of localized bright lines. These systemsare poor in the ability to provide sufficient contrast and brightnessfor gray-scale or full color imagery. In addition, the typical fortyfive degree tilt results in a rather bulky structure that not suitablefor installation in settings where compactness and intimacy might beimportant. Further, such systems have an extremely narrow field ofview—an observer directly in front of the screen can see the text orinformation, but an observer standing directly to one side or the othermay not, or at the very least will perceive a dramatically dimmer image.In addition, such displays can not be placed directly upon a backgroundobject such as a map or chart, without the background object then beingviewed at an undesirable angle.

Weight, thickness, durability, cost, aesthetic appearance and qualityare key considerations for display systems, including see-throughsystems. Hence, there is a need for a device that overcomes one or moreof the drawbacks identified above.

SUMMARY

In particular and by way of example only, according to an embodiment,provided is a see-through display, including: a see-through screenhaving a front side and opposite thereto a back side, the screenstructured and arranged to receive an image signal light and redirectthe image signal light into a range of angles, the range centered abouta normal to the screen, background image light transmitted generallythrough the screen with minimal scattering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a see-through display according to anembodiment;

FIG. 2 is an enlarged portion of the see-through display shown in FIG.1;

FIG. 3 is a side view of an alternative embodiment of a see-throughdisplay configured for front projection;

FIG. 4 is the side view of FIG. 2 further illustrating occluded areas;

FIG. 5 is a perspective view of a louver screen shown in FIG. 1according to an embodiment;

FIG. 6 is a partial side view of the louver screen shown in FIG. 5;

FIG. 7 is a plane view of the projected louver elements shown in FIG. 6;

FIG. 8 is an enlarged cross-section view of an alternative embodiment ofa louver screen;

FIG. 9 illustrates the optimal louver alignment angles andreflected/refracted components for incident light;

FIG. 10 is a top view of a louver element shown in FIG. 9;

FIG. 11 is a front view of a louver screen showing parallel rows oflouver members according to an embodiment;

FIG. 12 is a front view of louver screen showing curved rows of louvermembers according to yet another embodiment;

FIG. 13 a side view of a see-through display according to yet anotherembodiment;

FIG. 14 a side view of a see-through display according to still anotherembodiment;

FIG. 15 is a side view of a see-through display according to yet anotherembodiment;

FIG. 16 is a side view of a see-through display according to a furtherembodiment; and

FIG. 17 is a side view of a see-through display according to yet afurther embodiment.

DETAILED DESCRIPTION

Before proceeding with the detailed description, it is to be appreciatedthat the present teaching is by way of example, not by limitation. Theconcepts herein are not limited to use or application with a specificsee-through display. Thus, although the instrumentalities describedherein are for the convenience of explanation, shown and described withrespect to exemplary embodiments, it will be appreciated that theprinciples herein may be equally applied in other types of see-throughdisplay systems.

FIG. 1 conceptually illustrates a portion of a see-through display 100.In at least one embodiment, the see-through display 100 has asee-through screen 102 having a front side 104 and opposite thereto aback side 106, and a thickness 101 (Ts) therebetween. As shown in FIG.1, no visually obstructing frame, back or case is provided adjacent tothe back side 106 that would prevent an observer from seeing an object108 that is behind the transparent screen 102.

To facilitate the description, the orientations are referenced to thecoordinate system with three axes orthogonal to one another, as shown inFIG. 1. The coordinate system is chosen to be fixed to the screen 102.The axes intersect mutually at the origin of the coordinate system,which is chosen to locate at the center 150 of the front side 104 asindicated in the figures. The axes shown in all the figures are offsetfrom their actual locations, for clarity.

In a typical installation, the screen might be hung on a vertical wallfor viewing by observers standing up or sitting upright. In thisimplementation, the X-axis is chosen to be pointing in the verticaldirection with the positive direction of the X-axis pointing upwards.The axis that is pointing in the horizontal direction and isperpendicular to the front surface of the screen 102 is chosen to be theY-axis. Regardless of the actual orientation of the screen, the X-axishereafter might be referred to as the vertical axis. The direction alongthe X-axis hereafter might be referred as the vertical direction or theX-direction. The Y-axis hereafter might be referred to as thehorizontal-normal axis and the direction along the Y-axis as thehorizontal-normal direction or the Y-direction.

Moreover, the Y-coordinate, Y_(f), of front side 104 of the screenequals zero (0) and the Y-coordinate, Y_(b), of the back side of thescreen 106 is negative and equals −Ts. As shown in FIG. 1, thesee-through screen 100 divides the surrounding space into two regions:region 180 and region 190. The Y-coordinate is positive for all pointslocated in region 180. The Y-coordinate is negative and less than −Tsfor all points located in region 190. Region 180 may also be referred toas the front region or the front side. Region 190 may also be referredto as the back region or the back side. An observer in the front/backregion may also be referred to as a front/back observer. An object inthe front/back region may also be referred to as a foreground/backgroundobject.

The Z-axis is in the plane of the front side 104 surface and isperpendicular to the X-axis and the Y-axis. Hereafter, the Z-axis mightbe referred to as the horizontal-in-plane axis and the direction alongthe Z-axis as the horizontal-in-plane direction or the Z-direction. Thepositive Z-axis direction points to the observer's right when theobserver is facing the screen from the front side. A plane that containsthe X-axis and any planes parallel to it hereafter might be referred toas a vertical plane. In at least one embodiment, the screen is flat andis a thus vertical plane. Hereafter, the edges of the screen wouldsometimes be referred to as the right edge, the left edge, the top edgeand the bottom edge, based on the perspective of a front observer.

A plane that contains both the Y-axis and the Z-axis and any planesparallel to it hereafter might be referred to as a horizontal plane. Thepositions of the see-through screen and objects in the surrounding spacecan thus be conveniently expressed by their coordinates, for example,the center 150 of the front side 104 of the see-through screen 102 canbe referred as location X₀=0, Y₀=0 and Z₀=0 or conventionally (0,0,0).Unless otherwise specified, the positive directions of the axes areindicated by an arrowhead in the Figures.

The see-through display 100 of this invention allows a front observer,under favorable conditions, to see images displayed on the screen and tosimultaneously see background objects through the screen. In addition, aback observer can also, under favorable conditions, see images displayedon the screen and simultaneously see foreground objects through thescreen. The images displayed on the screen may be the same or differentfor the front and the back observers.

As is more fully described below, the screen is structured and arrangedto receive an image signal light 110 (presented as a collimated lightbeam) and redirect the image signal light into a range of angles Vr in avertical plane, the range centered about a normal 112 to the front side104 as shown in FIG. 1. Similarly, the signal light is redirected into arange of horizontal angles, Hr, in a horizontal plane. Hr is not shownin the figures. The ranges Vr and Hr might be tailored to be differentfrom each other to suit specific applications. For example Hr could betailored to be less than about ten degrees)(10° for private viewing andmade to be nearly one hundred eighty degrees)(180° for comfortableviewing in a home theater environment. In addition, background imagelight 114 is transmitted generally through the see-through screen 102with minimal scattering. Moreover, the transparent screen is structuredand arranged to combine the image signal light 110 with the backgroundimage light 114.

In at least one embodiment, background image light 114 originates asillumination light 116 passing through the see-through screen 102 fromthe front side 104 to strike a background object 108. In at leastanother embodiment, additional sources of illumination, such as source130 are placed at the same side, i.e., the back side of the see-throughscreen 102, as the background objects 108. Light ray 132 from source 130illuminates the background object 108 without passing through thesee-through screen 102. In another embodiment, the background image isself luminous such as a light bulb or a CRT display, not shown.Background object 108 reflects the illumination light 116 and 132 asbackground image light 114, which is viewable from the front side 104 byan observer. If background object 108 is self luminous, background imagelight 114 may emanate from background object 108, for viewing from thefront side 104 by an observer. In addition, the majority of ambientlight 126 impinging upon the front side 104 is directed generallytowards the back side 106. The structural details of the see-throughdisplay 100 are described further below.

Likewise, ambient light incident upon the back side 106 is directedgenerally towards the front side 104 without redirection towards anobserver. It is to be understood and appreciated that the light rays110, 114 and 116 undergo a slight change of direction governed by theFresnel law of refraction at the interfaces. For ease in illustrationand discussion, light rays 110, 112, 114 and 116 are shown as generallystraight when crossing interfaces.

In the embodiment as shown, the see-through display 100 is a rearprojection display 100. An image source 118 is provided and opticallycoupled to the back side 104 of see-through screen 102. Image source 118for a rear projection system may be any device capable of providing afocused image on back side 106 of the screen, such as, for example, aprojector. As is further discussed below, image source 118 provides animage in the form of image signal light 110 at an angle 160 that issubstantially smaller than ninety degrees) (90° relative to screen 102,as shown in FIG. 1. In FIG. 1 this is accomplished in part by providingthe image source 118 below the see-through screen 102.

Background image light 114 emanates from background objects 108 atlocations separate and apart from image source 118. Further, ambientlight 126 and 132 may be provided by at least one ambient source (notshown) at one or more locations separate and apart from the image source118. More specifically, image source 118 provides image signal light 110from a discreet origin that is separate and apart from a second andthird location, e.g., the source locations of background image light 114and/or ambient light 126 and 134 (when source 130 is an ambient lightsource).

In at least one embodiment the screen 102 consists of a transparentlayer 120 and a plurality of louver members 122 at least partiallydisposed within the transparent layer 120. As in at least oneembodiment, the louver members 122 are physical structures, theassembled structure may be referred to as a louver screen 124. Thesurfaces of the louver members 122 facing the imaging source 118 arecapable of reflecting and redirecting the incoming light 110 into acontrolled orientation, as described in further details below.

As is further appreciated with respect to FIGS. 2 and 3 the louverscreen 124 may be configured to provide a rear projection system, seeFIG. 2, or a front projection system, see FIG. 3. With respect to eachconfiguration, FIGS. 2 and 3 show a cross-sectional view of thesee-through display 100 in the X-Y plane.

Referring to the FIGS. 2 and 3, the angles, such as θ₄ of light rays 110from image source 118, or θ₅ of light rays 136 emanating from objectslocated in back region 190, are measured with respect to the positiveY-axis. Angles, such as θ₆, of light rays, such as 110 emanating fromimage source 118 located in the front region 180 are measured withrespect to the negative Y-axis. Angles of the physical structures suchas louver members 122 are measured with respect to the positive Y-axis.A positive angle is obtained by a counter clockwise rotation from therespective reference Y-Axis. For example, in FIGS. 2 and 3, angles θ₁and θ₅ are positive angles, while angle θ₃ and θ₆ are negative angles.In the context of this invention, the angles are confined to the rangebetween negative ninety degrees and positive ninety degrees (−90° and90°).

As shown in FIGS. 2 and 3, louver members 122 (of which members122A˜122F are exemplary) are oriented at angle θ₁. Vector line 200connecting the first end A of louver member 122B and the second end B ofneighboring louver member 122C is oriented at angle θ₂. Vector line 202connecting the first end A of louver member 122B and the second end B ofneighboring louver member 122A is oriented at angle θ₃. In at least oneembodiment, louver members 122 are physical structures of thin filmmaterial that can reflect and redirect incident light. The properties ofthe louver members 122 are further discussed below.

Background object 108 in the back region 190 reflects incident light 131from an ambient light source, such as light source 130. In at least somesettings, it is understood and appreciated that a background object mayemit light, such as, for example, when the background object is a lightbulb. Through either reflection of ambient illumination or selfemission, light rays, such as ray 136, from the background object 108propagate to and impinge upon the back side 106 of the see-throughscreen 102 at an angle θ₅. When light ray 136 falls within the angularrange bounded by vectors 200 and 202, i.e., when θ₃<θ₅<θ₂, light ray 136passes through the see-through screen 102 without being intercepted bylouver members 122 and being redirected or absorbed.

Light rays 114 (FIG. 1) and 136 can subsequently be observed by anobserver located in the front region 180. The background object 108 isvisible within the viewing angle θv which is defined by the equationθv=θ₂−θ₃. Moreover, an observer in the front region 180 can see thebackground objects in the back region 190 through the see-through screen102 when within the range of angles bounded by vectors 200 and 202, whenthe background object 108 emanates or reflects rays 136 that are alsowithin the bounded range of vectors 200 and 202. This range of anglesmay be referred to as the see-through angular range. Through thereciprocity principle of optics, an observer in the back region can seean object in the front region within the same angular range.

Within this visible angular range, θv, portions of the background objectare still occluded by the opaque louver members 122, as shown by theshaded areas 400 in FIG. 4. Typically, the linear dimension L₁ of thelouver members along the X-axis is about one to one hundred (1-100)μm,and the center to center spacing between adjacent louver members isabout one to ten (1-10) times the linear dimension L₁ of the individuallouver members 122. Moreover, there is a clear spacing L₂ betweenneighboring louver members 122. These linear dimensions are chosen sothat an observer located at an observing distance from the displaycannot resolve the individual louver members. In at least oneembodiment, the observing distance is typically a distance of about zeropoint two meters or more (≧0.2 m).

The occlusion will show up in the first order as a reduction in thebrightness of the background image 108. A fraction, R_(t) of the lightimpinging on the see-through screen 102 in the horizontal normaldirection is transmitted straight through without being redirected bythe louver members 122. R_(t) equals L₂/(L₁+L₂) and may be referred toas the transmission ratio. In at least one embodiment, L₁ equals L₂ andalong the horizontal normal direction, the see-through screen 102transmits 50% of the light from background object 108 through thesee-through screen 102 to observers in the front region 180. Maximumtransmission of light rays 136 from a background object 108 occurs whenthe ray angle θ₅ is equal to θ₁. The transmission ratio can be tailoredfor different applications by varying the dimension L₁ and L₂. Toachieve maximum see-through properties for see-through screen 102, it isdesirable that R_(t)>0.

Interference between the periodicity of the louver members 122 and thebackground object image may manifest as moiré fringes, which are wellknown in the field of optics. It is also appreciated that an observerlooking at the background object 108 through the see-through screen 102from a different physical location or angle will see a different set ofoccluded areas.

Outside of the see-through angular range, all light rays emanating fromor reflected by the background object 108 are intercepted by one or morelouver members 122. As such, the background object 108 is not visible toan observer in the front region 180 looking into the see-through screen102. In at least one embodiment, the louver members 122 are structuredwith one light reflecting side 402 and one light absorbing side 404 asshown in the enlargement of FIG. 4 bounded by dotted line 406. In suchan embodiment, the louver members 122 are physical structure, whereinside 402 is coated with a light reflecting material such as silver oraluminum, and side 404 is coated with Chromium Oxide (Cr2O3), Carbon andmaterials containing carbon, a carbon die or ink, Titanium, and or othermaterials with low reflectivity of visible light, and or light absorbingproperties. Combinations of these materials may also be used.

In at least one embodiment, as is further described below, the louvermembers 122 are established by depositing thin films. In such anembodiment, the absorbing and reflecting structure shown in theenlargement 406 may be accomplished by successive deposition of lightabsorbing and light reflecting materials.

In general, with embodiments utilizing the louver members 122 providingthe light absorbing side 404 and light reflecting side 402, the ambientlight source 130 is positioned such that light rays 134 emanating fromthe light source 130 and striking the back side 106 of the see-throughscreen 102 directly are absorbed by sides 162 or otherwise redirected bythe louver members 122 away from observers in the front region 180.

Referring back to FIGS. 1 and 2, in at least one embodiment, the imagesource 118 is placed at a location such that the image signal light 110impinges on the see-through screen 102 at an angle θ₄ or 160 that isoutside the see-through angular range, i.e., θ₄>θ₂ or θ₄<θ₃. In thiscase, all the light rays impinging on the back side 106 of see-throughscreen 102 from the image source 118 are intercepted by the louvermembers 122 and redirected toward observers in the front region 180.

Similarly, for a front projection system as shown in FIG. 3, the imagesource 118 is placed at a location such that the image signal light 110impinges on the see-through screen 102 at an angle θ₆ that is outsidethe see-through angular range, i.e., θ₆>θ₂ or θ₆<θ₃. In this case, allthe light rays impinging on the front side 104 of see-through screen 102from the image source 118 are intercepted by louver members 122 andredirected towards observers in the front region 180.

In at least one embodiment of a rear projection configuration as shownin FIGS. 1 and 2, θ₁=30°, θ₂=60°, θ₃=−30°, and θ₄=60°. The viewing anglethrough the see-through screen 102 is θ₂−θ₃=90°. In at least oneembodiment of a front projection system as shown in FIG. 3, θ₁=60°,θ₂=about 80°, θ₃=−60°, and θ₆=−30°. The viewing angle through thesee-through screen 102 is θ₂−θ₃=140°.

It is appreciated that for certain applications, a background object 108may be purposefully concealed. The background object 108, such as asecurity camera, is configured so as not to emit and/or reflect visiblelight towards the see-through screen 102. In addition, the ambient lightsources in the front region 180 and back region 190 are arranged so asto provide minimum illumination upon the security camera. As such, thesecurity camera will hardly be visible to an observer in the frontregion 190 even though it is located in the see-through angular range.

The nature of the louver screen 124 is further shown in FIGS. 5 through12. FIG. 5 conceptually illustrates an enlarged partial perspective viewof louver screen 124. In the embodiment shown, louver screen 124consists of a transparent layer 120 of material having a first side 500and opposite thereto a second side 502, and a thickness 504therebetween.

A plurality of louver members 122 are disposed within the transparentlayer 120, specifically, exemplary louver members 122A˜122F. Each louvermember 122 has a first end 506 and a second end 508. As shown, the firstend 506 of each louver member is adjacent to the first side 500. Thesecond end 508 of each louver member is proximate to the second side502. Moreover, each louver member 122 has a component 512 normal tofirst side 500, the component 512 being a fraction of thickness 504. Inaddition, each louver member 122 has a component 514 parallel to thefirst side 500, the component 514 being a fraction of thecenter-to-center spacing 516 between adjacent louver members 122, morefully described below with respect to FIGS. 5-7.

In at least one embodiment as shown, second end 508 defines a space 510between the second end 508 and the second side 502. In at least oneembodiment, this space 510 serves as added support and/or protection forlouver members 122. In an alternative embodiment, the second end 508 maybe substantially adjacent to second side 502 such that space 510 doesnot exist as an integral component of transparent layer 120. In suchembodiments, protection and/or support may be provided by an additionaltransparent layer joined to transparent layer 120 in the illustratedlocation of space 510.

In at least one embodiment the louvers 122 are reflective thin film witha thickness of about zero point one (0.1) μm deposited on a groovedsurface of the transparent layer 120 as shown in FIG. 8 (the groovessubsequently filled and planarized to provide smooth back side 106). Inanother embodiment, the louvers 122 may consist of a conglomerate ofreflective particles, each with a linear dimension of about one to onehundred (1-100) μm, closely packed and adhered to the grooved surfacesof the transparent layer 120. Filling the groves with a transparentmaterial and planarizing to provide back side 106 protects the louvermembers 122 and eliminates surfaces that might otherwise act as prisms.The material of reflective particles may be, for example, titaniumdioxide or aluminum oxide.

FIG. 6 is a side view of the louver screen 124 shown in FIG. 5,specifically showing the edge view of louver members 122A˜122F in the XYplane. FIG. 7 illustrates the projected components of the louver members122A˜122F onto a plane 700 that is parallel to the first side 500, i.e.,plane 700 is an XZ plane. Each louver member 122 has a projectedcomponent 600 in plane 700.

In at least one embodiment as shown, the projected second end 508A oflouver member 122A does not overlap the projection of the first end 506Bof adjacent louver member 122B, such that the projected component 600Ais a fraction of the center-to-center distance 602 between adjacentlouver members 122, e.g., louver members 122A and 122B as shown. Inother words, in at least one embodiment, the louver members 122 arearranged in non-overlapping rows relative to a normal to the front side104 (see FIG. 1), corresponding to the second side 502 in FIG. 5.Moreover, in at least one embodiment, there are transparent areas 702 inplane 700 between projected components 600.

As used herein, the term “transparent” is generally defined to includethe definitions of “capable of transmitting light so that objects orimages can be seen as if there were no intervening material,” and“easily seen through.” In at least one embodiment, transparent layer 120may be aptly described as translucent; in that transparent layer 120 maybe colored, polarized and/or intentionally diffusing.

Returning to FIG. 5, in at least one embodiment, the louver members 122are aligned to receive light entering the first side 500 from an anglethat is outside of the see-through angular range as described above,relative to the first side 500 and direct the light out the second side502 at a range of angles that is typically symmetrical about the Y-axis.

Each louver member 122 has a reflective surface 520. In at least oneembodiment this is a textured surface, and in an alternative embodimentit is a smooth surface. In another embodiment, the louver memberconsists of at least one layer of closely packed particles with lineardimensions of about one to one hundred (1-100)μm. The louver members 122may take many forms. Exemplary louver members 122A˜122B aresubstantially flat members. Exemplary louver members 122C˜122D includecylindrical mirror sections, e.g., a mirror segment 522 of louver member122C has a curved cross-section along the first side 500 and a straightcross-section along a side 524 of transparent layer 120. Exemplarylouver members 122E-122F include elliptical mirror segments, e.g.,mirror segment 526 of louver member 122F has a curved cross-sectionalong the first side 500 and a curved cross-section along side 524.

Moreover, in at least one embodiment, the louver members 122 are shapedlouver members. More specifically, in at least one embodiment, eachsurface 520 has at least one first curvature 528 along a first axis(e.g., Y-axis) and at least one second curvature 530 along a second axis(e.g., Z-axis) transverse to the first axis.

In addition, the shaped louver members 122 are grouped into at least onesubgroup, the shaped louver members 122 within the subgroup beingsystematically arranged in one embodiment, and randomly distributed inan alternative embodiment. Further, the size and shape of each shapedlouver member 122 may be smaller than each image pixel. Further still,in at least one embodiment, the shaped louver members 122 are providedby reflective particles rather than a continuous film of material.

As stated above, in at least one embodiment, at least one advantageousaspect of see-through display 100 is that the louver screen 124 isstructured and arranged so that each louver member receives the imagesignal from a source at a range of angles, which is typically less thanabout one degree (1°) and redirects the image signal into a range ofangles centered about a normal to the front side of the screen. FIGS.8˜10 are provided to further illustrate this aspect of see-throughdisplay 100. Multiple image sources may be used to construct abi-directional screen as described above.

FIG. 8 presents an enlarged cross-section view of an embodiment of alouver screen 800 in an XY plane. As shown, louver screen 800 has atransparent layer 120 shown to initially have a plurality of grooves802, each groove having at least a first surface 804 intersecting asecond surface 806. Louver members 808, of which louver member 808A˜808Care exemplary, are established in at least one embodiment by disposing areflective material upon each first surface 804. In at least oneembodiment, the reflective material is deposited on a fraction of firstsurface 804 as exemplified by louver member 808D. As stated above, thelouver members 808 may have a light reflecting side 402 and a lightabsorbing side 404 (see FIG. 4).

The second surface 806 is not coated and therefore remains transparent,and is thus shown as a dotted line. Following the establishment of thelouver members 808, the grooves 802 are filled with transparent materialand planarized to provide a substantially smooth side 106 (shown indotted relief) parallel to front side 104. It is of course understoodand appreciated that louver members 808 are substantially identical withlouver members 122; however, a different numbering convention has beenapplied in FIG. 8 for ease of discussion.

The relationship between the angle of incidence and the angle ofreflection by the louver members is conceptually illustrated in FIG. 9.With respect to FIG. 9, the relationship between φ₁, the incident angleof light from the image source, φ₂, the angle of the louver reflector,and φ₃, the nominal viewing angle, may be expressed by Equation 1 below:φ₁+2φ₂+φ₃=90°  Equation 1

The angles φ₁ and φ₂ are measured with respect to the negative X-axisand the angle φ₃ is measured with respect to the positive Y-axis. Thepositive directions of the angles are indicted by the arrow heads.Typically the screens are designed for the observers to view the screenaround a nominal viewing angle φ₃=0°. Examples of the orientations forthe louver mirrors to achieve this viewing condition are summarizedbelow:

-   For a front projector with an incident angle φ₁=30°, optimal    reflector angle is φ₂=30°-   For a rear projector with an incident angle of φ1=−30°, the optimal    reflector is φ₂=60°

Instead of a flat reflector, the reflecting surface of the louver may becurved to produce the ranges of viewing angles as indicated by theangular ranges Vr and Hr introduced earlier. Curved louvers arediscussed in further detail below.

FIG. 9 depicts a portion of a single louver member 808. In addition,louver member 808 is shown as not being embedded in the transparentlayer, and the light from imaging source 118 is not passing through thetransparent layer before striking the louver member 808. Thus theincident light form the image source 118 and the reflected light fromthe louver member 808 are assumed to be in the same optical medium, forexample air. As shown, single louver member 808 may be a component of afront projection embodiment as is further described below.

When the image light passes into the transparent layer before strikingthe louver member, as in FIG. 8, the light rays undergo an additionalchange of direction as they enter and leave the transparent layer by theamount shown in FIG. 9. These additional angular changes may becalculated and accounted for in the structure and arrangement of thelouver members in such embodiments so as to compensate for theseadditional changes in the directions of the incident and reflected lightrays. These additional angular changes are not shown in the otherfigures so as to minimize confusion.

Returning to FIG. 8, in at least one embodiment for a rear projectionsystem, the front side plane 104 is parallel to the back side 106 plane.The image signal light 110 impinges upon the back side 106 at an angle820 of about sixty degrees (60°) relative to normal 810′ that isperpendicular to the back side plane 106. Normal 810′ is also parallelto a normal 810 of the front side 104. Both normals 810 and 810′ areparallel to the Y-axis. To redirect the incident light into theY-direction, the louver members 808 are angled at about thirty degrees(30°) relative to 810″, shown as angle 652. This corresponds to thecondition where the incident angle φ₁=−30° and the louver angle φ₂=60°in FIG. 9.

In an alternative embodiment for front projection (not shown), the imagesignal light 110 impinges upon the front side 104 at angle of aboutsixty degrees (60°) relative to normal 810. The louver members 808 arealigned at about sixty degrees (60°) relative to normal 810 to the frontside 104. This corresponds to the condition where the incident angleφ₁=30° and the louver angle φ₂=30° in FIG. 9. The positive direction ofnormal 810 is indicated by the direction of the arrow, which is pointingto the right-hand side of the page. The positive direction is the samefor reference normals 810′ and 810″, each parallel to normal 810. InFIG. 9, angles φ₁, and φ₂ are measured with respect to the negativeX-axis, while angle φ₃ is measured with respect to the positive Y-axisof the Cartesian coordinate system defined earlier.

Louver member 808B has been illustrated as a curved louver member,specifically a vertical circular arc segment with an arc angle of aboutthirty degrees (30°). The plane tangent to the louver at the center ofthe louver member is oriented at an angle of about thirty degrees (30°)with respect to the normal 810′. As such, the incoming signal light110A˜110C is received at a single angle relative to the louver screen800 and redirected into a range of angles. More specifically, imagesignal light ray 110A is striking at about the center of louver member808B and is therefore directed through front side 104 in a directionapproximately normal to the surface of front side 104. Image signallight ray 110B is striking near the first end 506 of louver member 808Band is therefore directed through front side 104 at first angle 812.Image signal light ray 110C is striking near the second end 508 oflouver member 808B and is therefore directed through the front side 104at a second angle 814.

In at least one embodiment, the arc angle of the curved louver member isbetween about twenty to forty degrees (20°˜40°.) This curved louver willreflect a collimated light beam, such as those represented by the lightrays 110A, 110B and 110C, into a diverging beam that is spread betweenthe first and second angles 812 and 814. The angular divergence of thereflected beams 812 and 814 is between about twenty to forty degrees(20°˜40°) relative to normal 810, providing a vertical viewing range,Vr, which is depicted in FIGS. 1 and 10˜12 of about forty to eightydegrees (40°˜80°.)

FIG. 10 presents a top view of louver member 808B. The curve 808B shownin FIG. 10 depicts the intersection of the louver member with a YZplane, and is symmetrical about the Y-axis. In this view the imagesignal light 110 strikes the louver member 808B from an origin below theplane of the paper. The image signal light 110 is reflected by thelouver member and may emerge from the front side in a direction that isabove, below or in the plane of the paper. For simplicity ofillustration, FIG. 10 illustrates the projection of the incoming andexiting rays in the plane of the paper.

The following description of the ray traces applies to the projection ofthe light rays onto the plane of the paper, i.e., the YZ plane asindicated by the Cartesian coordinate axes. The incoming rays 110A, 110Band 110C are parallel to the Y-axis. The plane 820 that is tangent tothe center point of the intersecting curve 808B is perpendicular to theY-axis. Tangents 1000, 1002 at both the first end 1004 and the secondend 1006 of louver member 808B subtend an angle of forty-four degrees(44°) to the Y-axis as shown in FIG. 10. The projection onto the YZplane of the image signal light ray 110A strikes at about the center oflouver member 808B perpendicular to the surface and is thereforereflected back onto itself.

Image signal light ray 110B is striking near the first end 1004 oflouver member 808B and is directed off at a first angle 1008. Similarly,image signal light ray 110C is striking near the second edge 1006 oflouver member 808B and is directed off at a second angle 1010. Otherimage signal light rays are distributed over the surface of 808B and thereflected rays are distributed in between the extreme angles 1008 and1010. In at least one embodiment, the extreme angles, i.e., the firstand second angles 1008 and 1010, are both about eighty-eight degrees(88°), thus providing a horizontal viewing range, which is the sum ofangles 1008 and 1010, of about one hundred seventy six degrees) (176°).In another embodiment, 808B has a varying curvature across to tailor theangular intensity of the reflected beam. In yet another embodiment,varying curvature of 808B produces a total viewing angle, Vh, of onehundred eighty degrees (180°) and Lambertian distribution of angularintensity distribution.

Returning again to FIG. 5, louver members 122C˜122F are each illustratedas having four sections for ease of discussion and illustration. It isto be understood that each louver member may have one section or, asshown, may consist of many identifiable sections. The typical length ofthe sections, measured along a center curve, such as 530, is about tento two hundred (10-200)μm. Moreover, in at least one embodiment, eachsegment, e.g., 522 or 526, is a separate identifiable louver member. Inaddition, each louver member 122 may have a length about equal to thelength 532 of transparent layer 120, or a fraction thereof.

In at least one embodiment, the louver members 122 within louver screen124 are substantially identical. In yet another alternative embodiment,the louver members 122 within louver screen 124 may be different fromone to another, such as for example a mixture of flat and shaped louvershaving elliptical and/or cylindrical mirror segments, and/or a mixtureof louvers with different sized elliptical and/or cylindrical mirrorsegments with flat louvers, and/or a mixture of louvers with randomshapes and sizes. In other words, in at least one alternative embodimentthe plurality of louver members 122 may be sub-grouped, each sub-groupconsisting of at least one louver member. In such a configuration, theone or more members within each sub-group may be substantially identicalor different from one another, and may be substantially identical ordifferent from the members of another subgroup. In at least oneembodiment of such a configuration, a subgroup is a pixel of the screen.

In at least one embodiment, louver members 122 are physically reflectivesurfaces. More specifically, in one embodiment each louver member 122 isa light reflective material or is established from a light reflectivematerial such as metal (for example, without limitation, silver oraluminum) or a good reflector (for example, Titanium dioxide or aluminumoxide) or a conglomerate of fine particles made of these reflectivematerials. The size of the particles typically ranges from about one toone hundred (1-100)μm. Whether a physical structure or a coatedstructure, the light reflective material is sufficiently thick so as tobe non-light transmissive. In an embodiment utilizing silver oraluminum, the thickness of the silver or aluminum material may be aboutzero point one (0.1)μm thick.

In an alternative embodiment, louver members 122 are established from alight transmissive material having a different index of refraction fromtransparent layer 120. As the indices of refraction are different,louver members 122 will bend and/or reflect light in specific waysdepending on the angle of incidence of light provided through first side500.

In yet another alternative embodiment, louver members 122 are coatedwith a holographic film, or textured so as to provide physical reliefholograms. In at least one such embodiment, these hologram segments arecoated with reflective material to further augment the dispersion oflight.

In at least one embodiment, transparent layer 120 and, morespecifically, louver screen 124 is flexible. Such flexibility permitslouver screen 124 to bend or otherwise contort as may be desired incertain viewing locations and/or to withstand physical stress and/orabuse. In at least one embodiment, the flexibility permits louver screen124 to be rolled away when not in use. In at least one other embodiment,the louver screen 124 is flexible and attached to a transparent flexiblebacking to enhance the physical durability while maintaining theflexibility.

FIGS. 11 and 12 conceptually illustrate different arrangements of thelouver members. As shown in FIG. 11, in at least one embodiment, louvermembers 122 are arranged in straight parallel rows 1100 across louverscreen 124. An alternative embodiment is shown as FIG. 12, wherein thelouver members 122 are arranged in curved rows 1200 with equal spacingtherebetween. Image source 118 is positioned at a distance along theY-axis and oriented to direct image light into the plane of thesee-through display 100. Location 1202 is the projection of the locationof the projector onto the plane of the screen. In at least oneembodiment such as that shown in FIG. 12, the curved rows 1200 areconcentric to location 1202. Moreover, louver row 1204 is an arc sectionof circle 1206 having radius 1208 extending from center location 1202 atthe image source 118.

As shown in both FIGS. 11 and 12, background object 108 is visiblethrough louver screen 124. As such, it is appreciated that see-throughdisplay 100 may be employed in environments where it is desirable todisplay visual information to an observer while simultaneouslypermitting the observer to view background items such as object 108.

In light of the above description of louver screen 124, the conceptualdepiction of FIG. 1 may be more fully appreciated. Specifically, theapparent solid reflective surface provided by louver members 122 fromthe perspective of image source 118 insures that image signal light 110from image source 118 is directed towards an observer. Background imagelight (shown as thick dotted arrows 114) incident upon the back side 106of the louver screen 124 is transmitted through the louver screen 124between the louver members 122 with minimal scattering. Background light114 has a small probability of encountering the louver members 122 andbeing redirected. Even so, the majority of the background light 114passes directly through louver screen 124 to reach the eye of anobserver.

In addition, the majority of ambient light 126 incident upon the frontside 104 of louver screen 124 (or the back side 106) passes throughlouver screen 124 between the louver member 122. Ambient light 126 alsohas a small probability of encountering the louver members and beingreflected.

In the event that background image light 114 or ambient light 126encounters a louver member 122, the alignment of louver members 122 issuch that background image light 114 or ambient light 126 is, ingeneral, reflected in a direction either toward the back side 106 of thescreen 102, or back out of the front side 104, but in a direction awayfrom the observer instead of back towards the observer.

In at least one embodiment, the first or the front side 104 and the backside 106 of screen 100 are both smooth and will reflect a fraction ofthe background image light 114 or ambient light 126. In at least oneembodiment, an antireflective coating is applied to the front side 104and/or back side 106 so as to reduce the amount of reflected ambientlight.

It is also to be appreciated that see-through display 100 may be placeddirectly upon (i.e., in intimate contact with) a background object, suchas a map, chart, picture or other image. For example, see-throughdisplay 100 may be placed upon a map so as to provide an observer with anavigation route. As shown in FIGS. 12, 13, due to the front and backsides 104, 106 being parallel and smooth, as well as the scale andperiodicity of the louver members, there is appreciably no parallaxerror in viewing the background object 108. Placing the see-throughdisplay 100 in intimate contact with the background object 108 will alsonot result in appreciable parallax error.

FIG. 13 illustrates an alternative embodiment of see-through display 100configured for front projection. Whereas in FIG. 3 the louver members122 are shown disposed proximate to the middle of the transparent layer120, in FIG. 13, the louver screen 1300 is substantially identical tothe louver screen 124 of FIG. 1, both in function and in structure. Asshown in FIG. 13, the orientation of louver screen 1300 has beenreversed such that the louver members 122 are adjacent to the front side104. Image signal light 110 provided by image source 118 is againprovided at angle 160 (corresponding to angle θ₆ in FIG. 3), and as suchmay encounter an apparent solid reflective surface provided by louvermembers 122.

Background image light 114 reflected from object 108 and incident uponthe back side 106, has a greater chance of passing through the louverscreen 1300 between louver members then encountering louver members 122.In other words, the majority of background image light 114 incident uponthe back side 106 is transmitted through the front side 104 with minimalscattering. As background image light 114 emerges from front side 104 itis effectively combined with the redirected image signal light 110, suchthat an observer perceives the visual image transmitted by image signallight 110 superimposed upon background object 108.

And again, ambient light 126 incident upon either the front side 104 orthe back side 106 generally travels through see-through display 100without redirection towards the observer. Ambient light 126 thatencounters louver members 122 is generally directed away from anobserver. In at least one embodiment louver screen 1300 is flexible, soas to permit, for example, roll away storage of see-through display 100.

To further assist image signal light 110 in reaching louver members 122and background image light 114 to pass through louver screen 1300, anantireflection coating as described above may be disposed upon the frontside 104 and the back side 106. Such an antireflection coating may alsoreduce the reflection of ambient light 126 incident upon front side 104;however, the improved contrast of see-through display 100 and reducedambient reflection is principally due to ambient light 126 passingthrough louver screen 1300 without reflection to the observer.

FIGS. 14 and 15 illustrate alternative embodiments of see-throughdisplay 100 wherein the image source 118 provides image signal light 110to the bottom of the transparent layer 120, rather than to either thefront side 104 or the back side 106. With respect to FIGS. 14 and 15,louver screens 1400, 1500 are similar to louver screen 124, 1300 ofFIGS. 1 and 13, respectively; however, the thickness 504 (see FIG. 5) oftransparent layer 120 is considerably greater. More specifically, thethickness is sufficient to accommodate presentation of all image signallight 110 to the bottom surface 1402, 1502 of the louver screen 1400,1500. In addition, the bottom surface 1402, 1502 is angled so as to beperpendicular to central light ray 110C presented from image source 118.

As shown, light rays 110 travel from the image source, through thebottom surface 1402, 1502 and strike louver members 122. Morespecifically, light rays 110 do not experience internal reflection fromthe front side 104 or the back side 106; rather, they travel in agenerally straight path from the image source 118 to the louver members106.

Background image light 114 reflected from object 108 and incident uponthe back side 106, has a greater chance of passing through the louverscreen 1300 between louver members then encountering louver members 122.In other words, the majority of background image light 114 incident uponthe back side 106 is transmitted through the front side 104 with minimalscattering. As background image light 114 emerges from front side 104 itis effectively combined with the redirected image signal light 110, suchthat an observer perceives the visual image transmitted by image signallight 110 superimposed upon background object 108.

Once again, ambient light 126 incident upon either the front side 104 orthe back side 106 generally travels through see-through display 100without redirection towards the observer. Ambient light 126 thatencounters louver members 122 is generally directed away from anobserver. With either embodiment as shown in FIG. 14 or 15, to furtherassist image signal light 110 in reaching louver members 122, anantireflection coating as described above may be disposed upon the frontside 104 and/or the bottom surface 1402, 1502.

In the above described embodiments the images projected upon thesee-through screen 102 and redirected by the louver members 122 arevisible by viewers only on one side, typically in the front region 180as illustrated. FIGS. 16 and 17 illustrate yet other alternativeembodiments for two-way or bi-directional see-through louver screens1600, 1700.

As shown in FIG. 16, a single image source 118 provides image signallight which is redirected to observers in both the front region 180 andrear region 190. Such dual redirection is achieved with two sets oflouver members 1602 and 1604 disposed within transparent layer 120 whichmore or less equally split the image signal light 110 and redirect itinto positive and negative Y-axis directions.

Each set of louver members 1602, 1604 is substantially identical tolouver member 122 as described above. As described above, each set oflouver members 1602, 1604 is structured and arranged to receive an imagesignal light 110 (presented as a collimated light beam) and redirect theimage signal light into a range of angles Vr in a vertical plane. In thecase of the louver members 1602, the range is centered about a normal112 to the front side 104. In the case of the louver members 1604, therange is centered about a normal 1606 to the back side 106.

In at least one embodiment, louver members 1602 are disposed adjacent tothe front side 104 of the see-through louver screen 1600 and louvermembers 1604 are disposed adjacent to the back side 106 of thesee-through louver screen 1600. In at least one embodiment, the louvermembers 1602 (the front set) are oriented at θ_(1f)=60° and redirect theimage light 110 from the image source 118 towards the front observer.The louver members 1604 (the back set) are oriented at θ_(1b)=−30° andredirect the image light 110 from the image source 118 towards the backobserver.

As in FIG. 3, image source 118 is placed in front of the see-throughscreen 1604 and configured to provide image signal light 110 at angleθ₆=−60°. The linear dimension, L, of the louver members 1602, 1604 alongthe x-axis is about twenty five (25)μm. The periodicity is about everyone hundred (100)μm. The distance 1606 between the sets 1602, 1804 isabout eighty five (85)μm. In such a configuration, about seventy fivepercent (75%) of the light of a background object will transmit throughthe see-through screen 1604 in the Y-direction. The distance between thesets of louvers is chosen such that all image signal light 110 isintercepted and substantially equally divided for redirection towardsobservers on either side of the see-through louver screen 1600.

FIG. 17 presents yet another alternative embodiment for thebi-directional see-through display utilizing a front image source 1702and a rear image source 1704. Image sources 1702, 1704 are substantiallyidentical to image source 118 as described above. In this embodiment,one image may be presented to an observer in the front region 180 and adifferent image may be presented to an observer in the back region 190.For the embodiment shown, the angles of projection are θ_(1b)=−60° andθ_(1f)=60°. In this instance, the louver members 1706 (the front set)are oriented at θ_(1f)=60°, and the louver members 1708 (the back set)are oriented at θ_(1b)=−60°.

As in FIG. 16, each set of louver members 1706, 1708 is substantiallyidentical to louver member 122 as described above. As described above,each set of louver members 1602, 1604 is structured and arranged toreceive an image signal light 110 (presented as a collimated light beam)and redirect the image signal light into a range of angles Vr in avertical plane. In the case of the louver members 1706, the range iscentered about a normal 112 to the front side 104. In the case of thelouver members 1708, the range is centered about a normal 1710 to theback side 106.

With respect to sets of louver members 1602, 1604 and 1706, 1708, thesignal light is also redirected into a range of horizontal angles, Hr,in a horizontal plane. Hr is not shown in the figures. The ranges Vr andHr might be tailored to be different from each other to suit specificapplications. For example Hr could be tailored to be less than about tendegrees (10°) for privacy and made to be nearly one hundred eightydegrees (180°) for comfortable viewing in a home theater environment.

It is understood and appreciated that alternative locations for eachimage source may be selected, such as, for example, one or both beinglocated above the screen rather than below it. In addition, as describedabove, each image source may in actuality be composed of multiple imagesources, such as for example red, green and blue projectors.

As shown in FIGS. 16 and 17, it is preferred that the louver members1602, 1604, 1706, 1708 be entirely embedded within the transparent layer120. Such embedment provides substantially smooth front and back sides104, 106 to the see-through louver screens 1600, 1700, and thusminimizes distortion and displacement of the background image whichcould be caused by prism effects when the front side 104 and back side106 are not parallel. For optimum utilization of the light output fromeach image source, the image sources are typically placed outside thesee-through angular range as described above such that all image lightpropagating to the see-through screen is intercepted by the louvermembers and redirected towards the observers.

In the configuration shown in FIG. 17, each image source is within thesee-through zone of either set of louver members. The spacing betweenthe sets of louver members 1706, 1708 and the transparent spacingbetween neighboring louver members can be adjusted to obtain one hundredpercent utilization of the image signal light as provided by each imagesource.

With respect to both FIGS. 16 and 17, it is understood and appreciatedthat an observer in the front region 180 may perceive the visualinformation provided by the image signal, as well as view backgroundobjects located in the back region 190. Likewise, an observer in theback region 190 may perceive the visual information provided by theimage signal as well as view what are from his or her perspective,background objects located in the front region 180. Each observer mayalso perceive the other observer.

Changes may be made in the above methods, systems and structures withoutdeparting from the scope hereof. It should thus be noted that the mattercontained in the above description and/or shown in the accompanyingdrawings should be interpreted as illustrative and not in a limitingsense. The following claims are intended to cover all generic andspecific features described herein, as well as all statements of thescope of the present method, system and structure, which, as a matter oflanguage, might be said to fall therebetween.

What is claimed is:
 1. A screen, comprising: a first set of louver members at least partially disposed in the screen and located proximate to a first side of the screen, and a second set of louver members at least partially disposed in the screen and located proximate to a second side of the screen, wherein an observer on either side of the screen sees an image produced by light directed to that observer by the set of louvers on a same side of the screen as the observer; and wherein objects on an opposite side of the screen from the observer are visible to the observer between the louvers.
 2. The screen of claim 1, wherein the louver members each have a light absorbing side and a light reflecting side.
 3. The screen of claim 2, wherein the light absorbing side of the louver members is coated with materials selected from the group consisting of: chromium oxide, carbon, a carbon die, titanium, and combinations thereof.
 4. The screen of claim 1, wherein the louver members comprise a number of cylindrical mirror segments.
 5. The screen of claim 1, wherein the louver members comprise a number of elliptical mirror segments.
 6. The screen of claim 1, wherein the louver members are arranged in curved rows with equal spacing therebetween, in which the curved rows are concentric to an image signal source.
 7. The screen of claim 1, wherein the image signal light is evenly divided into a first and second portion and in which one of the first or second portion of image signal light is provided to observers on either side of the screen.
 8. The screen of claim 1, wherein the first set of louver member are configured to receive a first image signal light and the second set of louver members are configured to receive a second image signal light.
 9. A screen, comprising: a first set of louver members at least partially disposed in the screen and located proximate to a first side of the screen, and a second set of louver members at least partially disposed in the screen and located proximate to a second side of the screen, said first set of louver members being positioned to receive an image signal light and redirect that image signal light to an observer in front of the screen, said second set of louver members being positioned to receive an image signal light and redirect that image signal light to an observer in back of the screen, and wherein objects on an opposite side of the screen from an observer are visible to that observer between the louvers.
 10. The screen of claim 9, wherein the louver members each have a light absorbing side and a light reflecting side.
 11. The screen of claim 10, wherein the light absorbing side of the louver members is coated with materials selected from the group consisting of: chromium oxide, carbon, a carbon die, titanium, and combinations thereof.
 12. The screen of claim 9, wherein the louver members comprise a number of cylindrical mirror segments.
 13. The screen of claim 9, wherein the louver members comprise a number of elliptical mirror segments.
 14. The screen of claim 9, wherein the louver members are arranged in curved rows with equal spacing therebetween, in which the curved rows are concentric to an image signal source.
 15. The screen of claim 9, wherein the image signal light is evenly divided into a first and second portion and in which one of the first or second portion of image signal light is provided to observers on either side of the screen.
 16. The screen of claim 9, wherein the first set of louver member are positioned to receive a first image signal light and the second set of louver members are positioned to receive a second image signal light.
 17. A method of displaying an image on a screen, comprising: with a first set of louver members at least partially disposed in the screen and located proximate to a first side of the screen, directing light of a projected image to an observer on said first side of the screen, and with a second set of louver members at least partially disposed in the screen and located proximate to a second side of the screen, directing light of a projected image to an observer on said second side of the screen wherein objects on an opposite side of the screen from the observer are visible to the observer between the louvers.
 18. The method of claim 17, wherein the louver members are arranged in curved rows with equal spacing therebetween, in which the curved rows are concentric to an image signal source.
 19. The method of claim 17, further comprising: dividing the image signal light evenly into a first portion and a second portion; and directed said first portion of the image signal light to said first set of louvers and directing said second portion of the image signal light to said second set of louvers.
 20. The method of claim 17, further comprising: with the first set of louver members, receiving a first image signal light; and with the second set of louver members, receiving a second image signal light. 